This invention relates to digital imagesetting and, more particularly, to visual sensors for detecting imaging parameters.
Printing presses use plates to print ink onto paper and other media. One method used for creating plates is to expose photosensitive film with the matter to be printed. When the film is developed, the matter imaged on the film may be imaged onto a photosensitive plate, sometimes referred to as xe2x80x9cburningxe2x80x9d a plate. After processing, the plate can be used on a press to print the matter onto a medium. Part of the plate, usually the part defining the image to be printed, retains ink, while the other part of the plate does not. When the plate is introduced to ink and then to paper or other medium, the image is printed on the medium.
In a black and white printing job, there is usually one plate that is used to print black ink. In a color printing job, a different plate may be used for each color ink. A color job may use three colors of ink, usually cyan, magenta, and yellow, which in combination can be used to make other colors. A plate is usually produced for each color ink. Often, in addition to cyan, magenta, and yellow, black ink is also used. An additional plate is then required to print the black ink. Occasionally, one or more colors will be printed separately as well, referred to as a xe2x80x9cspot color.xe2x80x9d That color will also have its own plate.
Electronic prepress systems have used an imagesetter to receive raster data associated with a plate and to image the raster data onto photosensitive film. In this context, a raster may specify an image by pixels in columns and rows, at a predefined resolution. The film is then used to create a plate. The imagesetter exposes the photosensitive film pixel by pixel. One way that imagesetters image the raster data is to scan a laser across and down a piece of film. Electronics control the laser to expose, or refrain from exposing, each pixel in the raster data. The imagesetter images the pixels on the film in a manner that is precise and repeatable. Recently, platesetters also have been used to create plates directly from raster data without the use of intermediate film. Imagesetters, platesetters and like print engines, including proofers, are also referred to generally as output devices and writing engines.
Modem output devices may write or record images on various media used in image reproduction, including but not limited to photo or thermal sensitive paper or polymer films, photo or thermal sensitive coatings, erasable imaging materials or ink receptive media mounted onto an image recording surface, polymer film or aluminum based printing plate materials. Such media are mounted onto a recording surface which may be planar or curved.
Conventional digital imagesetters include a raster image processor (RIP) which receives signals representing an image to be recorded on the applicable media and converts the signals into instructions to a scanner which scans the recording media to produce the desired image. It is the function of the RIP to process the received signals representing the image into a corresponding instruction set that can be understood by the scanner.
In an article entitled xe2x80x9cHow to Calibrate and Linearize an Imagesetter Using the Digital UGRA/FOGRA Wedgexe2x80x9d by Franz Sigg and David Romano, published in the Society for Imaging Science and Technology Proceeding of the Fourth Technical Symposium on Prepress Proofing and Printing, October 1995, pp. 88-92, which was co-authored by David Romano who is also a co-inventor of the invention described herein, the need for imagesetter predictability and repeatability is discussed. As noted in the article, most modem imagesetters require adjustment so that a pre-specified solid density associated with the media to be imaged is produced. In most cases, it is required that the imagesetter be adjusted until a solid density is obtained on the medium being recorded. A densitometer can be utilized to measure the density of a recorded image to ensure correspondence with the pre-specified density. A densitometer measure within the range 1.0-4.0 or more is generally considered a solid density.
In practice, there are many imaging parameters, including scanner intensity that can be adjusted to change the density of a recorded image. However, because the intensity adjustment does not guarantee that desired dot areas will actually be recorded on the medium, it has been proposed that linearization curves be utilized to further adjust the imagesetter to offset the dot gain on the medium recorded by the imagesetter which is typically experienced as the intensity of the scanner is increased. In this way, the size or number of dots within an image are modified so that the desired dot areas will actually be recorded on the imaged medium. However, utilizing linearization curves does not ensure proper exposure. Although the use of linearization curves, may result in proper dot areas, the adjustments made to obtain the desired density may also result in undesirable dot fringe or fog between the dots on the recorded medium.
In the above-referenced Sigg and Romano article, it is proposed that half-tone patterns formed of one-by-one, two-by-two and four-by-four pixel checkerboards be compared with a 50% half-tone patch to calibrate the imagesetter. More particularly, it was disclosed that the proper imagesetter exposure occurs when the three checkerboards and a 50% half-tone patch have the same darkness or tint and hence the same visual density.
In non-digital platemaking, its is well known to form continuous gray tone wedges with a plurality of continuous tone density patches on a separate sheet of medium to compare with a test or registration patch formed on the recorded medium to initially set the exposure of the platemaker and/or to confirm that teach individual sheet of recorded medium includes a test patch which matches the selected patch on the wedge. Such a wedge is depicted in prior art FIG. 1.
As shown in FIG. 1, the wedge 10 includes various continuous tone density patches 20 which are numbered 1-13 on the wedge. The densities of the respective patches vary from 0.15 D-0.195 D in steps of 0.15 D where D represents optical density. Other fields, which are not relevant for purposes of the present disclosure, are also included on the wedge 10. The patches 20 are formed on a medium 30 which is preferably of a material substantially similar to the medium to be production imaged and on which the test patch is to be recorded. The platemaker operator is instructed which of the particular step(s) on the wedge 10, and therefore which of the specific patch or patches within the continuous tone density patches 20 the test patch recorded on each piece of production medium must correspond to in order to be acceptable.
In a typical operational setting, a range of steps, e.g., 4, 5 and 6, might be designed for use in initially establishing the exposure setting for the platemaker or in monitoring the acceptability of recorded media and hence the repeatability of the platemaker. The wedge 10 provides a simple way in which to initially set the recorded media in non-digital platemakers. Although providing a rough indicator for initially establishing an acceptable platemaker exposure setting and for monitoring platemaker repeatability by ensuring that all recorded media is exposed at approximately the same level, the wedge 10 cannot ensure that the recorded test patch actually corresponds to a desired density. In any event, may of the operators now operating digital platesetters and imagesetters were trained on non-digital platemakers and are familiar with the use of the FIG. 1 wedge for quality control.
Density is an example of one imaging quality parameter. An output device may have several imaging parameters, including, but not limited to, focus, spot size, spot side lobe size, addressability, and pulse width modulation. Depending on the design of a writing engine, it may be possible to adjust imaging parameter settings with software configuration or by hardware configuration or adjustment. Some imaging parameters may be modified by the writing engine operator, other imaging parameters may be modified by field service, other imaging parameters are set in the manufacturing facility during production. It may not be possible to adjust a particular imaging parameter in a particular writing engine. The image qualification process for a writing engine often requires the output of many pages of photocopy and a substantial amount of time on copy measurement tools for interpretation. Media use and measurement time add cost to writing engine manufacturing and to maintenance and problem diagnosis.
In addition, proper exposure setup of some media, such as plate material, require a comparison of several variables simultaneously, some of which are difficult to measure on the media itself with traditional tools. Plate material setup must be optimized for on-press performance and not just for a density operating point on the media itself.
In general, in one aspect, the invention features a visual sensor having a plurality of portions including a first portion and a second portion. The sensor is able to detect the state of one or more imaging parameters such as exposure setting, pulse width modulation, focus, balance, spot size and shape, spot ellipticity, sidelobe size, sidelobe shape, and sidelobe amplitude, media transfer function and gamma, edge sharpness, dot gain, uniformity, ink receptivity, physical changes in the media, pattern dependent effects such as dot gain or tone resolution compared to the type of halftone used, and sensitivity to calibrated position or exposure errors. The first image portion has a first imaging characteristic, and the second image portion has a second imaging characteristic. Imaging characteristics are characteristics of an image, including, but not limited to apparent density level, tint, color, reflectivity, absorption, granularity or microstructure, size, shape, distribution, degree of randomness, structure, edge sharpness, and depth or dimension. One of the portions is less sensitive to one or more imaging parameters than the other portion so that the first image portion and the second image portion appear substantially similar at a desired range of imaging parameters, and appear different otherwise. The imaging characteristic of the first portion is distinguishable from the imaging characteristic of the second portion for one or more ranges of one or more imaging parameters, and is not distinguishable for the alternate range(s) of the one or more imaging parameters. A range can be a particular imaging parameter value, or a range that excludes one or more imaging parameter values.
Embodiments of this aspect of the invention include the following features. In one embodiment, the one of the first and second portions comprises a coarse tint and the other of the first and second portions comprises a fine tint. In one embodiment, the coarse tint is a (nxc3x97n) periodic pattern and the fine tint is a (mxc3x97m) periodic pattern such that (n greater than m). In another embodiment, the imaging parameter is at least one parameter chosen from the set of exposure setting, pulse width modulation, focus, balance, spot size, spot shape, spot ellipticity, sidelobes size, sidelobes shape, sidelobes intensity, media gamma, edge sharpness, dot gain, uniformity, ink receptivity of plate material, physical media changes, pattern dependent effects, sensitivity to position errors, and sensitivity to exposure errors. In one embodiment, the first and second imaging characteristics each comprise one or more characteristics chosen from the set of density, tint, color, reflectivity, absorption, granularity, microstructure, size, shape, distribution, randomness, structure, shape, edge sharpness, and depth. In another embodiment, one of the first and second portions comprises a symbol and the other of the first and second portions comprises a background. In another embodiment, the symbol comprises at least one alphanumeric character. In another embodiment, the symbol is a shape chosen from the set of arrow, circle, square, rectangle, triangle, diamond, pentagon, and octagon. In another embodiment, the symbol is chosen to provide information related to the at least one imaging parameter setting range.
In another aspect, the invention features a method for imaging a visual sensor. The method includes defining an image having a first portion and a second portion proximate to the first portion. The first portion has a first imaging characteristic, and the second portion has a second imaging characteristic such that one of the first and second portions is less sensitive to an imaging parameter than the other of the first and second portions. The method includes imaging the image such that the first portion and the second portion appear substantially similar for at least one desired imaging parameter setting range and appear different otherwise.
In one embodiment, one of the first and second portions comprises a coarse tint and the other of the first and second portions comprises a fine tint. In another embodiment, the coarse tint is a (nxc3x97n) periodic pattern and the fine tint is a (mxc3x97m) periodic pattern such that (n greater than m). In another embodiment, the imaging parameter is at least one parameter chosen from the set of exposure setting, pulse width modulation, focus, balance, spot size, spot shape, spot ellipticity, sidelobes size, sidelobes shape, sidelobes intensity, media gamma, edge sharpness, dot gain, uniformity, ink receptivity of plate material, physical media changes, pattern dependent effects, sensitivity to position errors, and sensitivity to exposure errors. In another embodiment, the first and second imaging characteristics each comprise one or more characteristics chosen from the set of density, tint, color, reflectivity, absorption, granularity, microstructure, size, shape, distribution, randomness, structure, shape, edge sharpness, and depth. In another embodiment, one of the first and second portions comprises a symbol and the other of the first and second portions comprises a background. In another embodiment, the symbol comprises at least one alphanumeric character. In another embodiment, the symbol comprises a shape chosen from the set of arrow, circle, square, rectangle, triangle, diamond, pentagon, and octagon. In another embodiment, the symbol is chosen to provide information related to the at least one imaging parameter setting range.
In another aspect, the invention features an array of visual sensors. The array includes two or more sensors, each sensor having a first portion having a first imaging characteristic and a second portion proximate to the first portion having a second imaging characteristic. The imaging characteristic of one of the first and second portions is less sensitive to an imaging parameter than the imaging characteristic of the other of the first and second portions, such that the imaging characteristic of the first portion and the second portion appear substantially similar for at least one imaging parameter setting range and appear different otherwise. The plurality of sensors are imaged at at least two different imaging parameter settings. In one embodiment, one of the first and second portions comprises a coarse tint and the other of the first and second portions comprises a fine tint. In one embodiment, the coarse tint is a (nxc3x97n) periodic pattern and the fine tint is a (mxc3x97m) periodic pattern such that (n greater than m). In another embodiment, one of the first and second portions is an aperiodic pattern. In another embodiment, one of the first and second portions is imaged using random screening. In one embodiment, the imaging parameter is at least one parameter chosen from the set of exposure setting, pulse width modulation, focus, balance, spot size, spot shape, spot ellipticity, sidelobes size, sidelobes shape, sidelobes intensity, media gamma, edge sharpness, dot gain, uniformity, ink receptivity of plate material, physical media changes, pattern dependent effects, sensitivity to position errors, and sensitivity to exposure errors. In one embodiment, the first and second imaging characteristics each comprise one or more characteristics chosen from the set of density, tint, color, reflectivity, absorption, granularity, microstructure, size, shape, distribution, randomness, structure, shape, edge sharpness, and depth. In one embodiment, one of the first and second portions comprises a symbol and the other of the first and second portions comprises a background. In one embodiment, the symbol is chosen to provide information related to the at least one imaging parameter setting range.
In another aspect, the invention features a method for imaging an array of sensors. The method includes imaging a sensor by defining an image having a first portion and a second portion proximate to the first portion. The first portion has a first imaging characteristic and the second portion has a second imaging characteristic such that one of the first and second portions is less sensitive to an imaging parameter than the other of the first and second portions. The method includes imaging the image so that the first portion and the second portion appear substantially similar for at least one desired imaging parameter setting range and appear different otherwise. The method further includes modifying the imaging parameter after the sensor is imaged, and repeating the imaging and modifying steps for a range of imaging parameter values.
In one embodiment, one of the first and second portions comprises a coarse tint and the other of the first and second portions comprises a fine tint. In another embodiment, the coarse tint is a (nxc3x97n) periodic pattern and the fine tint is a (mxc3x97m) periodic pattern such that (n greater than m). In another embodiment, one of the first and second portions is an aperiodic pattern. In another embodiment, one of the first and second portions is imaged using random screening. In another embodiment, the imaging parameter is at least one parameter chosen from the set of exposure setting, pulse width modulation, focus, balance, spot size, spot shape, spot ellipticity, sidelobes size, sidelobes shape, sidelobes intensity, media gamma, edge sharpness, dot gain, uniformity, ink receptivity of plate material, physical media changes, pattern dependent effects, sensitivity to position errors, and sensitivity to exposure errors. In another embodiment the first and second imaging characteristics each comprise one or more characteristics chosen from the set of density, tint, color, reflectivity, absorption, granularity, microstructure, size, shape, distribution, randomness, structure, shape, edge sharpness, and depth. In another embodiment, one of the first and second portions comprises a symbol and the other of the first and second portions comprises a background. In another embodiment, the symbol is chosen to provide information related to the at least one imaging parameter setting range.
In another aspect, the invention features a method for calibrating an imagesetter using an array of sensors. The method includes imaging a sensor by defining an image having a first portion and a second portion proximate to the first portion. The first portion has a first imaging characteristic and the second portion has a second imaging characteristic such that one of the first and second portions is less sensitive to an imaging parameter than the other of the first and second portions. The method further includes imaging said image such that the first portion and the second portion appear substantially similar for at least one desired imaging parameter setting range and appear different otherwise. The method further includes modifying the imaging parameter after the sensor is imaged, repeating the imaging and modifying steps for a range of imaging parameter values, and determining a preferred imaging parameter value based on the similarity of the first and second portions.
In another aspect, the invention features a control wedge. The control wedge includes a plurality of blocks filled with different grayscale halftones, and a visual sensor having a first portion having a first imaging characteristic and a second portion proximate to the first portion having a second imaging characteristic. The imaging characteristic of one of the first and second portions is less sensitive to an imaging parameter than the imaging characteristic of the other of the first and second portions, such that the imaging characteristic of the first portion and the second portion appear substantially similar for at least one imaging parameter setting range and appear different otherwise.
The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description and from the claims.